This invention relates to muscle stimulation systems for paralyzed persons. More particularly, this invention relates to a stimulation system for producing a grasping action by a paralyzed hand.
Typical prior art devices for stimulating paralyzed muscles are described in Petrofsky et al U.S. application Ser. No. 444,647, filed Nov. 26, 1982 and in other references cited therein. These prior art systems have a set of three electrodes for each muscle group to be stimulated. The electrodes are placed on the surface of the skin above the muscle group to be stimulated and are excited by pairs of pulsed stimulation signals. One of the three electrodes is connected to a high voltage ground, and voltage pulses are applied between that electrode and the other two electrodes in alternating fashion. The series of pulses applied between the ground electrode and one of the active electrodes occur at a frequency of about 60 Hz, and these pulses are alternated with 60 Hz pulses applied between the ground electrode and the other active electrode. The pulse width is disclosed as being about 500 microseconds, and the pulse amplitude varies in accordance with the desired stimulation level up to a maximum of about 255 volts. Such stimulation produces recruitment of all motor units and results in maximum effort by the muscle. Feedback signals are provided in order to control the amplitude of the applied stimulation signals in an automatic manner.
The above-described stimulation technique has been used heretofore only for stimulation of leg muscles. Leg muscles have been so stimulated for operation of exercise equipment, for pedaling vehicles and for walking. Prior to this invention no attempt has been made to apply such techniques to arm or hand muscles. The present invention enables stimulation of the hand of a quadriplegic person to grasp and hold an object such as a drinking glass, a comb, a toothbrush or a fork.
Quadriplegic persons often times owe their condition to some type of accident which has produced spinal cord injury. If the injury occurs farther down on a spinal cord, only the legs are paralyzed, and a paraplegic condition results. Injuries at a higher point in the spinal cord produce various degrees of immobilization of the arms and hands. It sometimes happens that the arms and shoulders can be moved and that the hands while paralyzed, have retained the sense of touch. In other cases there is no sense of touch in the hands. This invention relates to both of the above-mentioned types of quadriplegia.